Shelf



FIG. 1 is a top front perspective view of a shelf showing my new design;

FIG. 2 is a front view thereof;

FIG. 3 is a right side view thereof;

FIG. 4 is a left side view thereof;

FIG. 5 is a top view thereof;

FIG. 6 is a bottom view thereof; and,

FIG. 7 is a rear view thereof. 

The ornamental design for a shelf, as shown. 